DR-white measures double-strand break repair pathways in Drosophila melanogaster. Jeannine R. LaRocque, Margot Le Neveu, Anthony Do. Department of Human Science, School of Nursing and Health Studies, Georgetown University, Washington, DC 20057.

   A DNA double-strand break (DSB) can result from both exogenous sources and endogenous cellular byproducts. Failure to repair these breaks results in genomic instability that may lead to cell death, mutations, cancer, and aging. DSBs are repaired by several mechanisms: error-free homologous recombination (HR) where an identical sequence is used as a template for repair, non-homologous end joining (NHEJ) where the ends of the DSB are modified and ligated, and single strand annealing (SSA) if the DSB occurs between two DNA repeats. In both yeast and mammalian cells, HR between diverged sequences is suppressed, preserving genomic integrity by preventing aberrant recombination products. DSB repair and the contribution of each repair pathway in the context of a whole genetically tractable organism has yet to be delineated. To address this, two novel reporter assays, DR-white and DR-white.mu, were integrated into the Drosophila genome. Phenotypic and molecular analyses using DR-white can detect induced DSB repair by NHEJ, HR, and SSA. DR-white.mu measures gene conversion tract lengths associated with HR and can also be used to detect NHEJ, HR, and SSA in the context of diverged sequences.
   We found that Drosophila repair simple DSBs predominantly by HR. Interestingly, gene conversion tract lengths are longer than those reported in mammalian cells. Additionally, HR repair between diverged sequences is suppressed, similar to levels measured in human cells. This work establishes this assay as a useful tool for measuring DSB repair in a whole organism and has the potential to address many future questions, including suppression of recombination between diverged sequences and the link between aging and DNA repair.